ST20-C1 datasheet(30/205 Pages) STMICROELECTRONICS

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4.1 Manipulating the evaluation stack

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Using ST20-C1 instructions

This chapter describes the purpose for which the sequential instructions are intended,

except for the multiply-accumulate instructions, which are described in Chapter 5.

These instructions are described in the context of their intended use. Some instruc-

tions are designed for use in a particular sequence of instructions, so this chapter

describes those sequences. Instructions for exceptions are described in Chapter 6

and multi-tasking instructions are described in Chapter 7.

The architecture of the ST20-C1, including the registers and memory arrangement, is

described in Chapter 3.

4.1

Manipulating the evaluation stack

The evaluation stack consists of the registers Areg, Breg and Creg. The general

action of the evaluation stack is described in section 3.3.1.

Instructions are provided for shuffling and re-order ing the values on the evaluation

stack, as listed in Table 4.1.

rot pops the value from Areg off the evaluation stack and rotates it into Creg, and arot

pushes the value from Creg onto the stack.

rev swaps the Areg and Breg, and dup

pushes a copy of Areg onto the stack.

Table 4.2 shows how each of these affects the evaluation stack. Each row shows the

contents of the evaluation stack after one of these instructions is executed if the initial

values of the Areg, Breg and Creg are a, b and c respectively.

Many instructions leave the initial Areg in Creg. This value may be restored into the

Areg by using

arot.

Mnemonic

Name

rot

rotate stack

arot

anti-rotate stack

dup

duplicate stack

rev

reverse stack

Table 4.1 Evaluation stack manipulation instructions

Instruction

Areg

Breg

Creg

rot

arot

rev

dup

Table 4.2 Evaluation stack manipulation

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